The present invention relates to a gas turbine stationary blade of a steam-cooled type, and more specifically, a gas turbine stationary blade having an inter-stage seal between a bore thereof and a rotor.
In a conventional gas turbine stationary blade, a passage is provided in its hollow and a discharged air from a compressor or extraction gas is run in the passage. By doing this, the blade is cooled so that the blade metal temperature is maintained at a certain allowable value lower than the temperature of a main gas.
The inside space of the blade serves also as a cooling air passage in which an air curtain is formed by inter-stage sealing.
In the steam-cooled gas turbine stationary blade, moreover, steam is circulated in place of air that is used in a conventional blade.
In some gas turbine stationary blades that utilize steam for blade cooling, the used steam is discharged into the main gas without being recovered. Preferably, however, all the steam used for cooling should be recovered.
In order to recover all the used steam, it is necessary, as in the conventional arrangement, to supply inter-stage cooling air to the bore-side seal so as to form a curtain of a low-temperature gas, thereby preventing the main gas from leaking out into the seal.
The trailing edge of the blade is so thin that it is difficult to provide passage means for steam circulation with a given area therein. Also in the steam cooling system, the blade wall may be formed having holes that extends from the inside of the blade into the main gas so that air can be run through the holes.
Thus, a blade section of the steam-cooled gas turbine stationary blade must be provided with steam passages, air passage means for the trailing edge, and air passage means for inter-stage sealing.
While a trailing edge cooling portion of the stationary blade directly opens on the outlet side of the blade, sealing air must be kept at a pressure higher than the pressure on the upstream side of the blade. It is difficult, therefore, to join the passage means for the trailing edge cooling air and the inter-stage sealing air.
In order to integrate the air passage means to secure the necessary cross-sectional area, the thin trailing edge portion of the blade must be provided with a passage that is elongated in the chord direction. Thereupon, the cross-sectional area of the blade that requires air-cooling increases, so that the cooling air must be increased in quantity. Thus, the steam cooling effect is reduced.